In the operation of grate coolers there are frequently red (i.e. glowing hot) patches or strips on the surface of the material to be cooled, and their cause lies in insufficient cooling of these regions or zones of the layer of material to be cooled.
If the material fired in the preceding firing assembly is thrown off onto the grate cooler, then frequently the coarser pieces predominantly fall onto one side of the grate and the finer ones onto the other side. Since the air permeability of a coarse-grained bulk material is greater than that of a fine-grained material and the cooling air stream seeks the path of least resistance the finer material is frequently insufficiently cooled in the grate cooler. On the other hand, a longer time is required in order to cool the coarser pieces through to the core.
In the operation of a grate cooler care should also be taken to ensure not only that the hot material delivered should be sufficiently cooled but also that as much heat as possible should be quickly extracted from the hot material and then returned to the preceding firing apparatus via the cooling air which is thereby heated. Therefore quality of a cooler is measured in the first instance by its degree of recuperation which constitutes a measure for its heat recovery.
The object of the invention is to provide a method and apparatus for cooling granular material on an air permeable grate in such a way that a degree of recuperation is achieved which is substantially improved by comparison with the prior art and thus the cooling material discharge temperature is also lowered further.